Activation and conformational changes of mushroom polyphenoloxidase by high pressure microfluidization treatment

Activation and conformational changes of Mushroom polyphenoloxidase (PPO) after high pressure microfluidization treatment were observed by means of UV spectra photometer, far-UV circular dichroism, fluorescence emission spectra, UV absorption spectra and sulphydryl groups detection. The results indicated that, treated under pressures of 90 MPa, 110 MPa, 130 MPa and 150 MPa one pass, and 150 MPa 1, 2 and 3 passes, respectively, mushroom PPO exhibited an increase in activity. The circular dichroism (CD) analysis demonstrated that some of secondary structures such as a-helix were destroyed. There were some indices that the increase of relative activity was accompanied by a decrease in a-helix content. The fluorescence emission spectra analysis indicated that Trp and Tyr residues in mushroom PPO were more or less exposed to solvent, and the result was in good agreement with that of UV absorption spectra analysis. The sulphydryl groups detection showed that the sulphydryl groups content on the surface of mushroom PPO was increased. Industrial relevance: Results of the present study show that high pressure microfluidization can not be used to inactivate mushroom PPO. However, it provides a new way for enzyme preparation, such as enzyme modification, with higher activity. High pressure microfluidization can be easily operated, with shorter treatment time and higher food safety compared with chemical methods. (C) 2008 Elsevier Ltd. All rights reserved.